Feedback shift registers are known in the art. In cryptographic applications, feedback shift registers are used in order to generate, in a pseudo-random manner, a sequence of values. Feedback shift registers (FSR) may generally be subdivided into nonlinear feedback shift registers (NLFSR) and linear feedback shift registers (LFSR). Especially nonlinear feedback shift registers are used as a basic security primitive in many types of stream ciphers. Furthermore, they are also used in deterministic random number generators (DRNG), and in on-chip security countermeasures of security controllers such as the means for generating masks for the protection against side-channel attacks (SCA) and probing attacks.
It is possible to mount side-channel and probing attacks against implementations of NLFSRs if these are not protected accordingly. A well-known mathematical countermeasure against SCA and probing are secret sharing schemes (SSS), which is also known as masking in the field of SCA. Applying an SSS to linear functions, e.g. linear circuit nets and linear feedback shift registers, is a trivial task. Applying SSS to nonlinear functions is a non-trivial field of research.